Build: Convert buildsystem base to modern cmake

Alters root cmake file and configuration files, and adds cmake toolchain
files.

WARNING: This change will not build in isolation, it requires _all_
other cmake changes to successfully build. It is split out only for
clarity of changes.

Signed-off-by: Raef Coles <raef.coles@arm.com>
Change-Id: Iecc914859a5b1d497176ec82f0b6c22764c7b556
24 files changed